1. Field of the Invention
The present invention relates generally to transcutaneous systems, and more particularly, to an external coil assembly of an transcutaneous system.
2. Related Art
The use of implantable medical devices to provide therapy to individuals for various medical conditions has become more widespread as the advantages and benefits such devices provide become more widely appreciated and accepted.
Medical devices designed for temporary or permanent implantation include, for example, cardiac assist or replacement devices such as pacemakers, defibrillators, circulatory assist devices and artificial hearts; stimulating devices such as Cochlear™ implants, neuromuscular simulators, bone growth stimulators. etc; biosensors, and others. Most implantable medical devices that perform work (active devices) and many of those that do not (passive devices) require power.
For those that require more power than can reasonably be provided by an implantable energy storage device, power must be transferred to the implanted device during its operational life. Traditionally, a percutaneous lead has been used to effect such power transfer. However, due to the high incidence of infection and other drawbacks, inductively-coupled transcutaneous energy transfer (TET) systems are more commonly utilized to provide the requisite power to an implanted device. Transcutaneous systems have also been utilized to transfer data additionally or alternatively to power.
A variety of arrangements have been developed or proposed for transcutaneous transmission of data or power. For example, in addition to providing power, transcutaneous energy and information transmission (TEIT) systems are used to transfer data utilizing the inductively-coupled coils or a separate, integrated device such as an infra-red (IR) communication device. For example, in some Cochlear™ implants a radio frequency link is established between the coils of a transcutaneous system to transmit encoded stimulus information to an internal receiver that delivers the stimuli to electrodes implanted in the cochlear. These and other systems which include the use of inductively-coupled coils are generally and collectively referred to herein as transcutaneous systems.
Generally, the subcutaneous coil is implanted just beneath the surface of the skin, while the external coil is located on the skin surface in alignment with the implanted coil. Because efficient energy transfer requires the coils to be aligned, various approaches have been developed to maintain such alignment between the external and implanted coils. Such previous approaches include ear hooks, headgear, pegs, VELCRO™, clips, skin pouches, and other mechanical alignment systems. These approaches suffered from poor alignment and increased possibility of infection. More recently, these approaches have been surpassed with the use of attractive magnets fixed relative to the internal and external coils. For example, in Cochlear™ implants, an internal coil and magnet are surgically secured to the cranium while the external coil is held on the scalp in alignment with the implanted coil by a magnet.